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How to Sew A Fly


A fly closure is a type of placket (page link) with an overlapping opening and either a button or zipper closure, usually at the center front of a garment. Fly closures can be cut as an extension of the front or as separate pieces sewn to the opening. An extension inside the fly opening protects your skin from the zipper teeth. This type of closure is strong and sturdy, so it works well on pants and jeans. On the outside of the garment, a topstitching line (page link) outlines the fly closure.

Fly closure

Fly closure

Inside of fly closure

Inside of fly closure


Fly closures are most often seen on trousers, jeans, pants, suit pants and shorts. You may see fly closures on jean-style skirts, but they tend to be reserved for pants and shorts. The fly is sewn while the front and back pieces are flat, and afterward, the crotch seam is sewn. On men’s garments, the fly laps with the left side over the right, and on women’s garments, the fly laps with the right side over the left. However, on jeans and casual pants, you may see the left side of the fly on top, as they were originally designed for men. Either side is fine. You may be used to unzipping your pants with the left side on top if you wear jeans often, so that might feel the most natural to you.

Tips + Notes

  • Shorten your zipper from the top, not the bottom. It’s easy to trim off the top of the zipper tape after the waistband is sewn to the top edge. Just be sure to wait to zip up the zipper until the top ends are enclosed in the waistband.
  • For a more subtle look, sew only one row of fly topstitching. For a more obvious look, or if the rest of the garment has two rows of topstitching, sew two rows of fly topstitching.


There are many different ways to sew a fly closure, but this is my favorite method. In this example, the fly extension as well as the fly facing are cut as separate pieces. I find this gives a nicer result to the fly opening. The fly facing is interfaced but the fly extension is not. On the left side of the front, the seam allowance should have a 3⁄8″ (1 cm) extension, so the zipper is sewn well inside the fly opening and won’t peek out. You’ll need to have a notch on the front opening where the fly closure is to stop on both sides of the front. You’ll also need two notches at the top edge of the right front showing where the fly extension is going to fall: one at the seam allowance and one 3⁄8″ (1cm) in from the seam allowance. Sew the crotch seam up to the notch for the fly opening, leaving it open above the notch, and finish the seam allowances separately.

How to sew a fly (1)

Interface (page link) and finish the long curved edge of the fly facing. Finish the edge with bias binding (page link) if desired. Sew the fly facing to the right front of the garment, right sides together, starting at the top edge and stopping at the notch. Ideally this stitching will stop right at the start of the crotch seam with no space in between. Understitch (page link) the fly facing, trim seam allowances and press.

How to sew a fly (2)

Fold the fly extension along the fold line, right sides together, and sew across the lower edge. Trim seam allowances, turn right side out and press. Finish the long raw edges together.

How to sew a fly (3)

Sew the zipper to the fly extension, face up, lining up the closed end of the zipper with the notch. Let any extra zipper extend over the top edge, and do not trim until zipper is enclosed in the waistband seam.

How to sew a fly (4)

Sew the fly extension to the left front using a zipper foot, stopping at the notch. Turn and edgestitch (page link) close to the fold with a zipper foot.

How to sew a fly (5)

If the zipper is open, close the zipper. From the inside, line up the fly facing seam line on the right front with the second notch (the one that’s farther away) on the left front. Pin through the fly facing and zipper without catching the fly extension or front of the garment.

How to sew a fly (6)

Flip over and pin the remainder of the zipper tape to the fly facing. Sew two rows of stitching through the zipper tape, using a zipper foot.

How to sew a fly (7)

On the right side, draw in the fly stitching line with chalk or a marking pen. Start below the zipper stop and curve up toward the waist, drawing the straight line 1½” (4 cm) from the center. Topstitch (page link) through the front and facing only.

How to sew a fly (8)

On the inside, tack the fly extension to the fly facing by stitching back and forth through both layers. You could also sew a bar tack (page link) at the curve of the fly topstitching, through all the layers.

Source : The Sewtionary An A to Z Guide to 101 Sewing Techniques + Definitions
About the Author : Tasia ST. Germaine